Plutonium-cupferron complex and method of removing plutonium from solution



PLUTONIUM-CUPFERRON COMPLEX AND METHOD OF REMOVING PLUTONIUM FROM SOLUTION Herbert A. Potratz, Boulder, Colo., assignor to the United States 'of America as repretented by the United States Atomic Energy Commission No Drawing. Application November 39, 1944 Serial No. 555,991

9 Claims. (Cl. 260-4291) number of 93, known as neptunium (symbol Np).

This new element by radioactive decay is transformed states O through a half-life of 2.3 days to a further new element known as plutonium (symbol Pu) "having an atomic number of 94. The particular isotope of this second new element has a mass of 239. In addition certain other elements are formed as a result of fission of the uranium 235 nucleus such elements being referred to as fission fragments or, including radioactive decay products thereof, as fission products. The fission fragments or products are radioactive isotopes which may be included in two general element groups, a light fission fragment comprising elements having atomic numbers from about 35 to 46 such as bromine, krypton, rubidium, strontium, yttrium, zirconium, columbium, molybdenum, masurium, ruthenium, rhenium and a heavy fragment comprising elements having atomic numbers from about 51 to 60 such as antimony, tellurium, iodine, xenon, caesium, barium, lanthanum, cerium, praseodymium and neodymium. The fission fragments are usually present in radioactive form, usually having a very short half-life, and by radioactive decay many of the fission fragments form other short lived products. As a result the radioactivity of the mass of uranium remains at a high and very dangerous level for some time following the neutron bombardment. It is particularly desirable to separate the plutonium from the radioactive fission products thereby removing from the mass subjected to neutron bombardment the radioactive materials and particularly the light elements such as light metals having very short half-lives and consequently high radioactivities. Thus the product obtained by neutron bombardment of uranium after more or less aging during or after bombardment comprises a major portion of uranium together with minor portions rarely in excess of one or two percent by weight of fission products and element 94 together with more or less element 93. The recovery of element 94 in a concentrated form involves the separation of the element 94 from such a product without excessive loss of element 94.

The removal of fission products from the element 94 is of particular interest since they retain their radioactivity for a substantial time after the neutron bombard rnent. Such radioactivity is so intense that it is exceedingly hazardous to personnel engaged in Working therewith.

A further problem which is frequently encountered involves the removal of impurities which may be present in a plutonium concentrate in order to secure a more pure product. Such impurities may comprise residual uranium and/or fission products and/ or agent used to assist in the separation of the plutonium from the Z irradiated uranium and may include numerous lightelements including lithium, magnesium, sodium, calcium, silicon, beryllium, etc.

It is an object of the present invention to provide new compounds or complexes which are particularly useful as a means for effecting a suitable separation of the plutonium from aqueous media particularly solutions containing impurities.

It is a-further object of the present invention to provide a simple and efficient method of removing plutonium from aqueous solution, particularly in the presence of other substances.

In accordance with the present invention it has been found that a new and useful complex may be secured by reaction of a plutonium compound with cupferron in aqueous medium. This complex is insoluble in water or substantially so and may be separated from the aqueous solution by precipitation or by extraction with a water-immiscible organic solvent such as chloroform, benzene, toluene, xylene, ethyl ether, etc.

The process is particularly effective when applied to reaction of the cupferron with plutonium in the tetravalent state. However, a complex may be formed using trivalent or hexavalent plutonium.

The, exact nature of the plutonium compound with each of the above compounds is not definitely known. However, in view of the nature of the organic compounds used, it is believed that cupferron forms a complex with plutonium of a chelate type.

The probable chelate formula for plutonium cupferride (the plutonium salt of nitro-p-phenyl-hydroxylamine) formed from tetravalent plutonium would be:

The production of these complexes is extremely useful in affording a means whereby plutonium may be separated from impurities such as are present in neutron irradiated uranium or from light metals. Thus neutron irradiated uranium may be converted to a water soluble state and dissolved to form an aqueous solution, for example,-a nitrate solution. This solution may be treated to separate uranium from the plutonium. A suitable method involves adsorption of the plutonium from the uranium in which case a major portion of the fission products are removed with the plutonium. For example, a solution of irradiated uranyl nitrate may be treated to selectively reduce the plutonium to a lower valent state generally the trior tetravalent state by means of a suitable reducing agent. Lower valent plutonium (Pu+++ or Pu++++) may be oxidized to the hexavalent state by an oxidation potential of about 1.1 volts. Reduction of the plutonium to the lower valent state may be eitected by reducing agents which are listed above 1.1 volts in the Latimer and Hildebrand table of oxidation-reduction potentials. To secure a selective reduction of plutonium without excessive reduction of uranium, reducing agents having a reducing potential which is sufliciently low so as to preclude the reduction of hexavale'nt uranium are used. Suitable agents to accomplish this result include ferrous ion, uranous ion or hydroxyl amine hydrochloride. I

The solution containing reduced plutonium is then treated for removal of plutonium by contacting the solu-- tion with an adsorbent such as 'colu'mbic oxide (Cb O silica gel, bismuth phosphate, lanthanum fluoride orresinous condensation products of phenol sulphonic acid and formaldehyde or 'by precipitating a carrier bismuth phosphate or lanthanum fluoride in the solution. In such a process the adsorbent or carrier removes plutonium in reduced state togetherwith some quantity of the fission products. The plutonium is then removed from the carrier or adsorbent by dissolving or extracting the carrier with an acid particularly an inorganic acid to form an acid solution such as nitric acid solution containing to percent HNO A suitable description of such a process appears in an application of Stanley G. Thompson and Glenn T. Seaborg, Serial No. 478,570, filed March 9, 1943, now Patent No. 2,799,553, issued on July 16, 1957.

The resulting solution contains plutonium, fission prod ucts, some uranium and more or less of the ions of the adsorbent. The plutonium or a substantial portion thereof may be removed by formation of a water insoluble organic complex such as herein described. This complex is then precipitated or extracted with a solvent such as chloroform, benzene, ethyl acetate, carbon tetrachloride, aniline, hexyl alcohol, xylene, ethyl ether or other waterimmiscible organic solvent.

The water-immiscible organic solvents as used in the process of the present invention extract the plutonium organic complex from aqueous solutions either by actual solution in the solvent or by preferential wetting by the solvent. In case of preferential wetting, the plutonium complexes may appear as a suspension or precipitate in the organic solvent due to the fact that the plutonium complex is preferentially wetted by the solvent rather than the water. It is understood throughout this specification and claims that extraction by water-immiscible organic solvents includes extraction by either or both solvent action or preferential wetting action.

The formation of the complex may be effected by adding the cupferron or a solution thereof to the plutonium solution and permitting the mixture to stand, usually with continuous or intermittent agitation, for a suitable period of time for example, 48 hours. Heating is generally unnecessary.

The process of the present invention is illustrated by the following examples:

Example I.0.5 milliliter of 1 normal nitric acid solution containing 400 micrograms of plutonium in tetravalent state was shaken with 3 drops of an aqueous 6 percent cupferron and agitated periodically for 48 hours. A yellow brown precipitate was formed which was agglomerted by agitation with nitrogen. The precipitate was extracted from the supernatant liquor with chloroform using 5 extractions and 2-3 cubic centimeters of chloroform per extraction. Over 99 percent of the plutonium was recovered in the chloroform.

A similar removal of plutonium is secured from a solution containing uranium fission products and negligible quantities of fission products are removed with plutonium. When solutions containing plutonium and light metals such as sodium, lithium or magnesium dissolved therein are treated in accordance with this process over 99 percent of these light metals remains in the aqueous phase and substantially none is extracted with the plutonium.

Example 1I.The process of Example I was repeated using 0.5 milliliter of a 1 normal nitric acid solution containing 450 micrograms of plutonium in hexavalent state and 3 drops of an aqueous 6 percent cupferron. A white precipitate formed initially. This precipitate darkened rapidly and upon extraction with'chloroform was not distinguishable from the product of Example III, 92 percent of the plutonium was recovered in the chloroform extract.

A similar separation may be secured when the solution contains fission products without separating a material quantity of fission products.

Example Ill.An extraction was carried out with a similar procedure of Example 2 above but with ethyl ether as the organic solvent in place of chloroform. It was found that the results are equally good as chloroform.

Example I V.-20 milliliters of an aqueous solution of plutonium sulphate containing suflicient plutonium to give a count of about 70 alpha particles per minute and having a pH of 1.7 was adjusted to different pHs shown in the following table with 1:1 sulphuric acid. In each case the solution was cooled in an ice bath and three drops of freshly prepared aqueous 6 percent cupferron solution added and the mixture agitated over a period periodically for 48 hours. The solution was then extracted with 2-3 milliliters of chloroform. The extraction was twice repeated adding more chloroform each time. Results are shown in the following table:

Table I Although the present invention is particularly concerned with the production of compounds or complexes of the isotope 94 it is broadly applicable to the production of compounds and to the recovery of element 94 including all isotopes thereof. For example, deuteron bombardment of uranium results in formation of the isotope 94 Other isotopes of this element may be formed upon subjection to prolonged thermal neutron bombardment of high intensity. All isotopes may be treated as herein contemplated.

Although the present invention has been described with particular reference to the specific details of certain embodiments thereof it is not intended that such details shall be regarded as limitations upon the scope of the invention except insofar as included in the accompanying claims.

I claim:

1. The method of separating plutonium from fission products present in neutron irradiated uranium which comprises forming an acidic aqueous solution of plutonium containing fission products, reacting the plutonium with cupferron and removing the plutonium cupferride.

2. The method of'separating plutonium from fission products present in neutron irradiated uranium which comprises forming an acidic aqueous solution of plutonium containing fission products, reacting the plutonium with cupferron and extracting the plutonium eupferride with an organic solvent.

3. The method of separating plutonium from an aqueous solution which comprises reacting plutonium acidic aqueous solution with cupferron and separating the insoluble plutonium cupferride from the solution.

4. The method of separating plutonium from uranium in an aqueous solution thereof which comprises reacting the plutonium in acidic aqueous solution with cupferron and extracting the plutonium cupferride with an organic solvent which is immiscible with water.

5. The process of claim 4 wherein the solvent is chloroform.

6. The process of claim 4 wherein the solvent is ethyl ether.

7. The method of separating plutonium from an aqueous solution of plutonium containing impurities which comprises reacting in an acidic medium the plutomum with cupferron and extracting the plutonium cupferride with a water-immiscible organic solvent.

8. The process of separating plutonium from an aqueous solution containing impurities which comprises reacting in acidic medium the plutonium with cupferron and removing the plutonium cupferride.

9. The process of separating plutonium from an aqueous solution containing fission products present in neutron irradiated'uranium which comprises reacting in an acidic solution the plutonium with cupferron by adding a freshly prepared saturated solution of cupferron to the acidic solution and extracting the plutonium cupferride with successive portions of ethyl ether.

References Cited in the file of this patent UNITED STATES PATENTS 2,206,634 Fermi et al. Oct. 3, 1935 5 2,211,119 Hixson et al. Aug. 13, 1940 2,227,833 Hixson et a1. Jan. 7, 1941 OTHER REFERENCES Thorntom" Am. Jour. Sci., vol. 42, pp. 151-154 10 (1916).

Thornton: Chem. News, vol. 114, pp. 13, 14 (1916). Angeletti: Gass. Chim. Ital., vol. 51, No. I, pp. 285-288 (1921). 

1. THE METHOD OF SEPARATING PLUTONIUM FROM FISSION PRODUCTS PRESENT IN NEUTRON IRRADIATED URANIUM WHICH COMPRISES FORMING AN ACIDIC AQUEOUS SOLUTION OF PLUTONIUM CONTAINING FISSION PRODUCTS, REACTING THE PLUTONIUM WITH CUPFERRON AND REMOVING THE PLUTONIUM CUPFERRIDE. 